1. Field of the Invention
This invention relates to the deposition coating materials on substrate articles, and more particularly to cathode sputtering of high temperature materials using multiple targets to provide a high degree of coating composition control.
2. Description of the Prior Art
Cathode sputtering is a process known in the art for depositing material on the surface of a substrate article. Deposition of the material on the article combines the properties of the coating material with the properties of the substrate material to produce a composite structure with enhanced capabilities.
In the practice of the cathode sputtering process, a coating material on a sacrificial cathode is bombarded by ions moving in response to an electric field causing a transfer of energy to the surface atoms of the coating material. The energized surface atoms eject from the sacrificial cathode into a sputtering chamber where a portion of the ejected atoms is intercepted by the substrate to be coated. The intercepted atoms strike the surface of the substrate and adhere thereto. Repeated depositions on the atomic scale over a period of time produce an even, well adhered coating on the substrate. The deposition of high melting point materials, including even ceramics, has been achieved. Notwithstanding the apparent benefits of cathode sputtering, apparatus and techniques for satisfactorily applying thick, high temperature coatings, of controllable and variable compositions, of material within reasonable elapsed periods have not heretofore been developed.
Designers and manufacturers of gas turbine engines are expending substantial economic and personnel resources in search for new apparatus and procedures capable of rendering cathode sputtering suitable for the rapid deposition of high temperature coatings on parts having complex geometries.
Increasing gas turbine operating temperatures have resulted in the development of more complex coatings. Among the coating ingredients now contemplated are the precious metals of platinum and rhodium. The high cost of such elements makes it important that efficient deposition means and apparatus be developed to precisely control the deposition and composition of such coatings.
U.S. Pat. No. 4,090,941 which shares a common assignee with the present application describes a hollow cathode sputtering apparatus having particular utility in the coating of gas turbine parts. The contents of this issued patent is incorporated herein by reference.